Need some help troubleshooting Messaging API 429s during concurrent session creation

General Discussion
1

Need some troubleshooting help with a rate-limiting issue we are hitting while trying to validate our messaging channel capacity. We are running load tests against Genesys Cloud to determine the maximum concurrent chat sessions our infrastructure can handle before hitting platform limits.

Background

  • Tool: JMeter 5.6.2
  • Location: Singapore (Asia/Singapore timezone)
  • Target: Genesys Cloud Platform APIs
  • Goal: Simulate high-volume customer message ingestion to test WebSocket stability and API throughput.
  • Config: 500 threads, ramp-up 60 seconds, loop count infinite for 10 minutes.

Issue

When we push more than 50 concurrent threads creating new messaging sessions via POST /api/v2/messaging/sessions, the platform starts returning 429 Too Many Requests errors almost immediately. This happens even though the official documentation suggests much higher limits for this endpoint. The error response includes a Retry-After header, but the value is inconsistent, sometimes 1 second, sometimes 30 seconds.

The JMeter logs show a sharp drop in successful responses (201 Created) right after the concurrency threshold is crossed. We are not seeing any 5xx errors, just strict rate limiting. This is blocking our capacity planning because we cannot determine if the bottleneck is our network setup or a hard platform limit we are unaware of.

Troubleshooting

  • Verified OAuth tokens are valid and not expiring during the test window.
  • Checked Retry-After headers in the response; they vary significantly.
  • Reduced thread count to 50 and the test completes without 429s, confirming concurrency is the trigger.
  • Confirmed no IP-based blocks are active from our Singapore VPS.
  • Reviewed the platform_api rate limit documentation but found conflicting info on burst allowances for messaging endpoints.

Has anyone else hit these specific limits during load testing? Are there specific headers or pagination strategies we should be using to avoid triggering these 429s? Any advice on how to structure the JMeter test to respect these limits while still getting accurate throughput data would be appreciated.